In-Line SEM Evaluation Technique for Cu Pad Nanotopography for Hybrid Bonding Applications

Wafer hybrid bonding is an essential technology for 3D integration of semiconductors. This technology involves directly bonding Cu pads formed on wafers. Considering the bulging out of Cu during annealing, the height of the Cu pad is controlled to be recessed by a few nanometers from the SiCN dielectric layer using Chemical Mechanical Processing (CMP) process. In wafer bonding, significant recess amounts due to Cu galvanic corrosion and recess amount variations of Cu pads affect the bonding quality. Therefore, we have developed a Cu pad evaluation technique, specifically focusing on rapid inspection of corrosions and measurement of recess amount using in-line scanning electron microscope (SEM) equipped with four backscattered electron (BSE) detectors arranged in different orientations. Verification with 350 nm-sized pads confirmed the inspection of galvanic corrosion and the ability to measure height with a precision of 0.47 nm in root mean square errors. This SEM-based Cu pad inspection and measurement technique using four BSE detectors can be utilized for controlling Cu height in wafer bonding through CMP.